Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media |
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Authors: | E Salinas A Roca M Cruells F Patio D A Crdoba |
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Affiliation: | a Centro de Investigaciones en Materiales y Metalurgia, Universidad Autónoma del Estado de Hidalgo, Pachuca, Hidalgo, Mexico;b Departament d'Enginyeria Química i Metal.lúrgia, Universitat de Barcelona, 08028 Barcelona, Spain |
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Abstract: | A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H3O+, Ag+, Pb2+, Na+ and K+ in the alkaline “sites” and, Cu2+ and Zn2+ as a partial substitution of iron. The formula is: Ag0.001Na0.07K0.02Pb0.007(NH4)0.59(H3O)0.31]Fe3(SO4)2(OH)6. Some contents of franklinite (ZnO·Fe2O3), gunninguite (ZnSO4·H2O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model.The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula:NH4Fe3(SO4)2(OH)6(s)+3OH(aq)−→(NH)4(aq)++3Fe(OH)3(s)+2SO4(aq)2−.The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the OH−] and an activation energy of 77 kJ mol−1. In NaOH/CN− media, the process is of 0.8 order with respect to the OH− and 0.15 with respect to the CN−. The activation energy was 46 kJ mol−1. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation. |
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Keywords: | Alkaline decomposition Cyanidation Kinetics Ammonium jarosite |
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